Prism sheet

ABSTRACT

An exemplary prism sheet includes a transparent main body. The transparent main body includes a first surface and a second surface. The first surface and the second surface are on opposite sides of the main body. The first surface of transparent main body defines a plurality of first elongated arc-shaped grooves and a plurality of second elongated arc-shaped grooves. The first elongated arc-shaped grooves intersect with the second elongated arc-shaped grooves. The second surface defining a plurality of rectangular structures. Each rectangular structure defining four adjacent triangular pyramid depressions.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a prism sheet, particularly to a prism sheet employed in a backlight module.

2. Description of the Related Art

Referring to FIGS. 10 and 11, a typical direct type backlight module 100 includes a frame 11, a plurality of light sources 12, a light diffusion plate 13, and a prism sheet 10. The light sources 12 are disposed in an inner side of the frame 11. The light diffusion plate 13 and the prism sheet 10 are disposed on the light sources 12 above a top of the frame 11 in that order. The light diffusion plate 13 includes a plurality of diffusing particles (not shown) configured for diffusing light. The prism sheet 10 includes a transparent substrate 101 and a prism layer 103 formed on a surface of the transparent substrate 101. The prism layer 103 forms a plurality of elongated V-shaped ridges 105.

In use, light from the light sources 12 enters the diffusion plate 13 and becomes scattered. The scattered light leaves the diffusion plate 13 to the prism sheet 10. The scattered light then travels through the prism sheet 10 and is refracted out at the elongated V-shaped ridges 105 of the prism sheet 10. The refracted light leaving the prism sheet 10 is concentrated at the prism layer 103 and increases the brightness (illumination) of the prism sheet 10. The refracted light then propagates into a liquid crystal display panel (not shown) disposed above the prism sheet 10.

However, although light from the light sources 12 enters the diffusion plate 13 and becomes scattered, after the light leaves the prism sheet 10, strong light spot of the light sources 12 often occurs.

In order to reduce or eliminate the strong light spot of the light sources 12, the backlight module 100 should further include an upper light diffusion film 14 disposed on the prism sheet 10. However, although the upper light diffusion film 14 and the prism sheet 10 are in contact with each other, a plurality of air pockets may still exist around the boundaries of the light diffusion film 14 and the prism sheet 10. When the backlight module 100 is in use, light passes through the air pockets, and some of the light undergoes total reflection by the air pockets along one or another of the corresponding boundaries. In addition, the upper light diffusion film 14 may absorb a certain amount of the light from the prism sheet 10. As a result, a brightness of light illumination of the backlight module 100 is reduced.

Therefore, a new prism sheet is desired in order to overcome the above-described shortcomings.

SUMMARY

A prism sheet includes a transparent main body. The transparent main body includes a first surface and a second surface. The first surface and the second surface are on opposite sides of the main body. The first surface of transparent main body defines a plurality of first elongated arc-shaped grooves and a plurality of second elongated arc-shaped grooves in the first surface. The first elongated arc-shaped grooves intersect with the second elongated arc-shaped grooves. The second surface defining a plurality of rectangular structures. Each rectangular structure defining four adjacent triangular pyramid depressions.

Other advantages and novel features will become more apparent from the following detailed description of various embodiments, when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present prism sheet. Moreover, in the drawings, like reference numerals designate corresponding parts throughout several views, and all the views are schematic.

FIG. 1 is an isometric view of a prism sheet in accordance with a first embodiment of the present invention.

FIG. 2 is a side cross-sectional view taken along the line II-II of FIG. 1.

FIG. 3 is a side cross-sectional view taken along the line II-II of FIG. 1.

FIG. 4 is similar to FIG. 1, but showing a view of the prism sheet from another aspect.

FIG. 5 is a photo showing an illumination distribution test result of the prism sheet of FIG. 11.

FIG. 6 is a photo showing an illumination distribution test result of the prism sheet of FIG. 1.

FIG. 7 is a top plan view of a prism sheet in accordance with a second embodiment of the present invention.

FIG. 8 is a side cross-sectional view of a prism sheet in accordance with a third embodiment of the present invention.

FIG. 9 is a side cross-sectional view of a prism sheet in accordance with a fourth embodiment of the present invention.

FIG. 10 is a side cross-sectional view of a conventional backlight module.

FIG. 11 is an isometric view of the prism sheet in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the drawings to describe embodiments of the present prism sheet in detail.

Referring to FIGS. 1 through 4, in a first embodiment, a prism sheet 20 includes a main body 21. The main body 21 includes a first surface 201 and a second surface 203. The first surface 201 and the second surface 203 are on opposite sides of the main body 21. The first surface 201 defines a plurality of first parallel elongated arc-shaped grooves 204 and a plurality of second parallel elongated arc-shaped grooves 205. The first elongated arc-shaped grooves 204 intersect with the second elongated arc-shaped grooves 205, thereby forming an angle larger than 0 degrees. In the illustrated embodiment, the angle defined by the first elongated arc-shaped grooves 204 and the second elongated arc-shaped grooves 205 is 90 degrees. The intersecting of the first grooves 204 and the second grooves 205 forms a plurality of intersection spots 2010. Each two adjacent spots 2010 are connected by a wall 2012 extending from the first surface 203 to the bottom of the first grooves. The second surface 203 defines a plurality of rectangular structures 207 and each rectangular structure 207 defines four adjacent triangular pyramid depressions 206. Each side of the rectangular structure 207 is bordered with a side of another adjacent rectangular structure 207.

In the illustrated embodiment, a cross-section taken along a plane perpendicular to an extending direction of the first elongated arc-shaped grooves 204 is semicircular. The first elongated arc-shaped grooves 204 are distributed side by side in the first surface 201. A radius R defined by each first elongated arc-shaped groove 204 is preferably in the range from about 0.01 millimeters to about 2 millimeters. A pitch P of adjacent first elongated arc-shaped grooves 204 is in the range from about 0.025 millimeters to about 1 millimeter. A depth H of each first elongated arc-shaped groove 204 is in the range from about 0.01 millimeters to about 2 millimeters. Preferably, the parameters of the second elongated arc-shaped grooves 205 are the same to those of the first elongated arc-shaped grooves 204.

The triangular pyramid depressions 206 are closely connected. In each rectangular structure 207, the four triangular pyramid depressions 206 together with the sidewalls thereof cooperatively form a four-pointed star. The four-pointed stars are distributed in a matrix manner in the second surface 203.

In the illustrated embodiment, corresponding sidewalls on each side of adjacent depressions 206 sharing a same edge collectively form V-shaped ridges, namely, a plurality of first V-shaped ridges, a plurality of second V-shaped ridge, a plurality of third V-shaped ridges, and a plurality of fourth V-shaped ridge. The first V-shaped ridges extend along a first direction X1. The second V-shaped ridges extend along a second direction X2. The third V-shaped ridges extend along a third direction X3. The fourth V-shaped ridges extend along a fourth direction X4.

The first, second, third, and fourth V-shaped ridges intersect with each other and cooperatively define the triangular pyramid depressions 206. In addition, the first V-shaped ridges and the third V-shaped ridges intersect with each other and form a plurality of intersections. Each of the plurality of intersections also intersects the second V-shaped ridges and the fourth V-shaped ridges correspondingly.

The first direction X1 and the second direction X2 cooperatively define an angle θ₁, the second direction X2 and the third direction X3 define an angle θ₂, the third direction X3 and the fourth direction X4 define an angle θ₃, and the first direction X1 and the fourth direction X4 define an angle θ₄. The θ₁, θ₂, θ₃, θ₄, are 45 degrees.

A vertex angle β of the V-shaped ridge is in the range from about 80 degrees to about 100 degrees. A pitch of the first V-shaped ridges is in the range from about 0.025 millimeters to about 1 millimeter. In the illustrated embodiment, the relations of the first, the second, the third, and the fourth V-shaped ridges are determined by the formula: D₁=D₃=√{square root over (2)}D₂=√{square root over (2)}D₄, wherein D₁ represents a pitch of the first V-shaped ridges, D₂ represents a pitch of the second V-shaped ridges, D₃ represents a pitch of the third V-shaped ridges, and D₄ represents a pitch of the fourth V-shaped ridges.

A thickness T of the sheet 20 is in the range from about 0.4 millimeters to about 4 millimeters. The prism sheet 20 can be made of a material selected from the group consisting of polycarbonate, polymethyl methacrylate, polystyrene, copolymer of methyl methacrylate and styrene, and any suitable combination of those. A mold used to manufacture the prism sheet 20 includes a plurality of first elongated arc-shaped protrusions and a plurality of second elongated arc-shaped protrusions formed on a first side surface, and a plurality of triangular pyramid protrusions formed on a second side surface opposite to the first side surface. The first elongated arc-shaped protrusions and the second elongated arc-shaped protrusions are configured to form the first elongated arc-shaped grooves 204 and the second elongated arc-shaped grooves 205 on the first surface 201 of the prism sheet 20 and the triangular pyramid protrusions are configured to form the triangular pyramid depressions 206 on the second surface 203 of the prism sheet 20, such that both sides of the prism sheet can be produced at a same time per injection molding.

The prism sheet 20 can be employed in a backlight module (not shown) in such manner that the first surface 201 is facing light sources of the backlight module and the second surface 203 is farther away from the light sources. Light enters the prism sheet 20 via the first surface 201. Since the inner surfaces of the first elongated arc-shaped grooves 204 and the second elongated arc-shaped grooves 205 are curved and the inner surfaces of the triangular pyramid depressions 206 are slanted, incident light that may have been internally reflected on a flat surface, are refracted, reflected, and diffracted. As a result, light outputted from the second surface 203 is more uniform than light outputted from a light output surface of a conventional prism sheet. Strong light spots of the light sources seldom occurs. There is no need to add an extra upper light diffusion film between the prism sheet 20 and the liquid crystal display panel. Thus, the efficiency of light utilization is enhanced.

Referring to the table 1 below, test samples are provided.

TABLE 1 Test samples Condition 1 LED + prism sheet 10 2 LED + prism sheet 20

Referring to the FIGS. 5 and 6, which reflect the test results from the test conditions in Sheet 1, light emitting from the prism sheet 10 will form a relatively strong light spot as shown in FIG. 5; in contrast, light emitting from the prism sheet 20 will form a uniform surface light source shown in FIG. 6. The test result shows that light emitting from the prism sheet 20 is more uniform. Therefore, when the prism sheet 20 is employed in a backlight module, strong light spot of the light sources seldom occurs, more uniform light is achieved, and there is no need to add an upper light diffusion film between the prism sheet 20 and the liquid crystal display panel. Thus, the efficiency of light utilization is enhanced.

In addition, because the triangular pyramid depressions 206 form the first, the second, the third, and the fourth V-shaped ridges, light emitting from the second surface 203 would be concentrated in planes perpendicular to the first direction X1, the second direction X2, the third direction X3, and the fourth direction X4 respectively, thereby increasing the brightness (illumination) of the prism sheet 10 along a direction perpendicular to the second surface 203.

In addition, in contrast to the conventional prism sheet 10, the prism sheet 20 is integrally formed by injection molding technology. The prism sheet 20 has a better rigidity and mechanical strength than the conventional prism sheet because the prism sheet is formed as a whole unit integrally. Thus the prism sheet 20 has a relatively high reliability.

Referring to FIG. 7, a prism sheet 30 in accordance with a second preferred embodiment is shown. The prism sheet 30 is similar in principle to the prism sheet 20 of the first embodiment, the second surface 303 defines a plurality of rectangular structures 307 and each rectangular structure 307 defines four adjacent triangular depressions 306. The prism sheet 30 also defines a plurality of quadrilateral pyramids 308. Each side of the rectangular structures 307 is bordered with one side of one quadrilateral pyramid 308.

Referring to FIG. 8, a prism sheet 40 in accordance with a third preferred embodiment is shown. The prism sheet 40 is similar in principle to the prism sheet 20 of the first embodiment, a plurality of the triangular pyramid depressions 406 are defined in the second surface 403. However a top end of the V-shaped ridge is flat. Since the top end of the V-shaped ridges is flat, strength of the V-shaped ridges is enhanced. As a result, the prism sheet 40 has a higher reliability than a prism sheet with the V-shaped ridges, the top of which would be easily damaged in use.

Referring to FIG. 9, a prism sheet 60 having a first surface 601 and in accordance with a fourth preferred embodiment is shown. The prism sheet 60 is similar in principle to the prism sheet 20 of the first embodiment, however a cross-section taken along a plane perpendicular to an extending direction of the first elongated arc-shaped grooves is elliptical. It can be understood that, a cross-section taken along a plane perpendicular to an extending direction of the second elongated arc-shaped grooves (not labeled) also can be elliptical.

Finally, while the preferred embodiment has been described and illustrated, the invention is not to be construed as being limited thereto. Various modifications can be made to the embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims. 

1. A prism sheet comprising: a transparent main body comprising: a first surface defining a plurality of first elongated arc-shaped grooves and a plurality of second elongated arc-shaped grooves intersecting with the first elongated arc-shaped grooves, wherein a plurality of intersection spots are formed as the result of intersection of the first grooves and the second grooves, each two adjacent spots are connected by a wall extending from the first surface to the bottom of the first grooves; and a second surface being on the opposite side of the main body from the first surface, the second surface defining a plurality of rectangular structures, each rectangular structure defining four adjacent triangular pyramid depressions.
 2. The prism sheet as claimed in claim 1, wherein each of the plurality of the rectangular structures borders with four other of the plurality of the rectangular structures, and sidewalls on each side of adjacent depressions sharing a same edge collectively form a plurality of first V-shaped ridges extending along a first direction, a plurality of second V-shaped ridges extending along a second direction, a plurality of third V-shaped ridges extending along a third direction, and a plurality of fourth V-shaped ridges extending along a fourth direction, the first V-shaped ridges and the third V-shaped ridges intersect with each other and form a plurality of intersections, each of the plurality of intersections also intersect the second V-shaped ridges and the fourth V-shaped ridges correspondingly.
 3. The prism sheet as claimed in claim 2, wherein an angle defined by the first direction and the second direction, an angle defined by the second direction and the third direction, an angle defined by the third direction and the fourth direction, and an angle defined by the fourth direction and the first direction are 45 degrees.
 4. The prism sheet as claimed in claim 2, wherein a vertex angle of each of the V-shaped ridges is in the range from about 80 degrees to about 100 degrees.
 5. The prism sheet as claimed in claim 2, wherein at least one portion of the top end of the V-shaped ridge is flat.
 6. The prism sheet as claimed in claim 1, wherein the second surface further defines a plurality of quadrilateral pyramids, and each side of each of the plurality of rectangular structures borders with one side of one of the quadrilateral pyramids. 